Finished lubricants and greases used for various applications, including automobiles, diesel engines, natural gas engines, axles, transmissions, and industrial applications consist of two general components, lubricating base oil and additives. Lubricating base oil is the major constituent in these finished lubricants and contributes significantly to the properties of the finished lubricant. In general, a few lubricating base oils are used to manufacture a wide variety of finished lubricants by varying the mixtures of individual lubricating base oils and individual additives.
Numerous governing organizations, including original equipment manufacturers (OEM's), the American Petroleum Institute (API), Association des Consructeurs d' Automobiles (ACEA), the American Society of Testing and Materials (ASTM), the Society of Automotive Engineers (SAE), and National Lubricating Grease Institute (NLGI) among others, define the specifications for lubricating base oils and finished lubricants. Increasingly, the specifications for finished lubricants are calling for products with excellent low temperature properties, high oxidation stability, low volatility, and good additive solubility and elastomer compatibility. Currently only a small fraction of the base oils manufactured today are able to meet the demanding specifications of premium lubricant products.
Finished lubricants comprising highly saturated lubricating base oils in the prior art have either had very low levels of cycloparaffins; or when cycloparaffins were present, a significant amount of the cycloparaffins were multicycloparaffins. A certain amount of cycloparaffins are desired in lubricating base oils and finished lubricants to provide additive solubility and elastomer compatibility. Multicycloparaffins are less desired than monocycloparaffins, because they decrease viscosity index, lower oxidation stability, and increase Noack volatility.
Examples of highly saturated lubricating base oils having very low levels of cycloparaffins are polyalphaolefins and GTL base oils made from Fischer-Tropsch processes such as described in EPA1114124, EPA1114127, EPA1114131, EPA776959, EPA668342, and EPA1029029. Lubricating base oils in the prior art with high cycloparaffins made from Fischer-Tropsch wax (GTL base oils) have been described in WO 02/064710. The examples of the base oils in WO 02/064710 had very low pour points, between 10 and 40 weight percent cycloparaffins, and the ratio of monocycloparaffins to multicycloparaffins was less than 15. The viscosity indexes of the lubricating base oils in WO 02/064710 were below 140. The Noack volatilities were between 6 and 14 weight percent. The lubricating base oils in WO 02/064710 were heavily dewaxed to achieve low pour points, which would produce reduced yields compared to oils that were not as heavily dewaxed.
The wax feed used to make the base oils in WO 02/064710 had a weight ratio of compounds having at least 60 or more carbon atoms and compounds having at least 30 carbon atoms greater than 0.20. These wax feeds are not as plentiful as feeds with lower weight ratios of compounds having at least 60 or more carbon atoms and compounds having at least 30 carbon atoms. The process in WO 02/064710 required an initial hydrocracking/hydroisomerizing of the wax feed, followed by a substantial pour reducing step. Lubricating base oil yield losses occurred at each of these two steps. To demonstrate this, in example 1 of WO 02/064710 the conversion of compounds boiling above 370° C. to compounds boiling below 370° C. was 55 wt % in the hydrocracking/hydroisomerization step alone. The subsequent pour reducing step would reduce the yield of products boiling above 370° C. further. Compounds boiling below 370° C. (700° F.) are typically not recovered as lubricating base oils due to their low viscosity. Because of the yield losses due to high conversions the process requires feeds with a high ratio of compounds having at least 60 or more carbon atoms and compounds having at least 30 carbon atoms.
Finished lubricants containing GTL base oils with high weight percents of all molecules with at least one cycloparaffin function made from Fischer-Tropsch wax are described in WO 02/064711 and WO 02/070636. Both of these applications use the base oils taught in WO 02/064710, which are not optimal in that they have a ratio of monocycloparaffins to multicycloparaffins less than 15, viscosity indexes less than 140, and may have aromatics contents greater than 0.30 weight percent. WO 02/064711 teaches a 0W-XX grade engine oil and WO 02/070636 teaches an automatic transmission fluid. The 0W-XX grade engine oil of Example 3 in WO 02/064711 is made with a lubricating base oil having a ratio of monocycloparaffins to multicycloparaffins of 13, a viscosity index of 125, and it contains a fairly high level of viscosity index improver, 10.56 weight percent. The automatic transmission fluid of Example 6 in WO 02/070636 is made with a lubricating base oil having 0.8 weight percent aromatics and a viscosity index of 122.
Due to their high saturates content and low levels of cycloparaffins, lubricating base oils made from most Fischer-Tropsch processes or polyalphaolefins may exhibit poor additive solubility. Additives used to make finished lubricants typically have polar functionality; therefore, they may be insoluble or only slightly soluble in the lubricating base oil. To address the problem of poor additive solubility in highly saturated lubricating base oils with low levels of cycloparaffins, various co-solvents, such as synthetic esters, are currently used. However, these synthetic esters are very expensive, and thus, the finished lubricants blended with the lubricating base oils containing synthetic esters (which have acceptable additive solubility) are also expensive. The high price of these finished lubricants limits the current use of highly saturated lubricating base oils with low levels of cycloparaffins to specialized and small markets.
It has been taught in U.S. Patent Application 20030088133 that blends of lubricating base oils composed of 1) alkylated cycloparaffins with 2) highly paraffinic Fischer-Tropsch derived lubricating base oils improves the additive solubility of the highly paraffinic Fischer-Tropsch derived lubricating base oils. The lubricating base oils composed of alkylated cycloparaffins used in the blends of this application are very likely to also contain high levels of aromatics (greater than 30 weight percent), such that the resulting blends with Fischer-Tropsch derived lubricating base oils will contain aromatics at levels greater than 0.30 weight percent. The high level of aromatics will cause reduced viscosity index and oxidation stability.
What is desired are finished lubricants; comprising lubricating base oils with very low amounts of aromatics, high amounts of monocycloparaffins, and little or no multicycloparaffins, that have a moderately low pour point such that they may be produced in high yield and provide good additive solubility and elastomer compatibility. Finished lubricants with these qualities that also have excellent oxidation stability, low wear, high viscosity index, low volatility, and good low temperature properties are also desired. The finished lubricants should meet the specifications for a wide variety of modern lubricant specifications, including multigrade engine oils and automatic transmission fluids. The present invention provides these finished lubricants and the process to make them.